This invention relates to an airbag inflator, specifically to an improved hybrid airbag inflator having a low mass initiator and an ignition delay sequencer to provide a controlled rate of inflation.
It is known in the art that for proper function of an inflatable vehicle occupant restraint (airbag), a controlled rate of inflation is critical. If the airbag inflates too rapidly, the occupant faces the potential of serious injury from the sudden deployment. If the airbag inflates too slowly, the airbag will fail to prevent the occupant from colliding with the vehicle dashboard, windshield or other rigid surface.
In a simple pyrotechnic inflator, some control over the inflation rate can be achieved by tailoring the quantity, shape and the burn rates of the gas generator propellant. In the pure stored cold gas inflator, some control over the inflation rate may be accomplished using variable or sequentially opened flow restrictions. This is typically accomplished by using eroding nozzles or some mechanism to change the nozzle geometry, sometimes with the undesirable side effect of having mechanisms that are subject to the effects of the acceleration present before and during the collision during which the inflator is intended to function.
A hybrid type inflator is an inflator that uses a combination of stored pressurized gas and a pyrotechnic gas generator to inflate the airbag. Typical of the prior art hybrid inflator are U.S. Pat. No. 5,242,194 to Popek and U.S. Pat. No. 3,895,821 to Schotthoefer et al. U.S. Pat. No. 5,242,194 to Popek discloses a hybrid inflator in which a hollow piston rod with an attached circular cutter is driven by a pyrotechnic actuator to puncture the seal disk. Subsequently, the flame from the actuator is conducted through the hollow piston rod to initiate the solid propellant gas generator to provide additional gas flow. U.S. Pat. No. 3,895,821 to Schotthoefer et al. discloses a hybrid airbag inflator in which a gas generator is ignited first, and thereafter the output of the gas generator ruptures a closure disk to release the pressurized gas. Gas flow control of the prior art devices is generally achieved by dimensional control of the nozzle, manifold, diffuser and other fluid flow controls, and by tailoring the quantity of propellant and its burn surface geometry.
It is known in the art that, in addition to controlling the overall inflation rate, a staged flow comprising an initial low inflation rate followed by a controlled high inflation rate is desirable to address protection of the out-of-position occupant, particularly a child standing on the vehicle seat. The low initial inflation rate allows the bag to break out of its container and assume a deployed configuration without injuring the vehicle occupant. The subsequent controlled high rate of inflation then provides the required energy absorption to prevent occupant injury.
The prior art discloses several methods addressing the problem of staged flow of gases in a hybrid inflator. U.S. Pat. No. 5,226,561 to Hamilton et al. discloses a hybrid inflator in which an initial explosive charge propels a projectile through a seal disk to release the cold gas. Subsequently, a spring/firing pin mechanism, which provides a short delay, actuates a gas generating means to supply the hot gas. U.S. Pat. No. 5,031,932 to Frantom, et al. discloses an inflator in which a first pyrotechnic actuator punctures a seal disk and, after a predetermined delay, provided by a remote timer, a second actuator initiates the pyrotechnic gas generator.
None of the prior art inflator, however, disclose an apparatus capable of providing an optimum delay between the onset of cold gas flow and the onset of the gas generator flow, without also having the added expense and complexity of multiple pyrotechnic initiators, or complex mechanisms that are subject to inertial effects during a collision. What is needed then is an airbag inflator that provides a staged gas flow without the complexity of the prior art multiple initiator or mechanical delay mechanism designs.